HVDC Network : DC fault ride-through improvement

This paper compares the transient behaviour of two HVDC networks with similar structures but which use different converter topologies, namely two-level and H-bridge modular multilevel converters. The key objective of this comparison is to show that the use of HVDC converters that inherent dc fault reversed blocking capability is beneficial to the HVDC networks in term of dc fault ride-through capability improvement (may reduce the risk of converter stations damage from over-current during dc side faults). The improvement in the HVDC network dc fault ride-through capability is achieved by stopping grid contribution to the fault current, and minimization of the transient component due to discharge of the dc side capacitors. Therefore HVDC networks that use converter stations with dc fault reversed blocking capability are expected to recover swiftly from dc side faults compared to those using converter stations without dc fault reversed blocking capability. To illustrate the outcomes of this comparison, the responses of both HVDC networks are examined when subjected to dc side faults. Issues such as lead-through and inrush currents in the ac and dc sides during and following dc faults are discussed

North Sea offshore modelling schemes with VSC-HVDC technology : control and dynamic performance assessment

The present thinking and trend for connection of large offshore wind farms, dispersed over wide areas, is to use multi-terminal HVDC networks rather than point-to-point DC transmission systems. The aim behind this approach is to improve the security of supply and minimise the loss of generation during scheduled maintenance or unexpected disturbances in any part of the power network. This paper describes various models of multi-terminal HVDC networks connecting offshore wind farms to a number of mainland AC grids which have been developed in MATLAB-Simulink with the main objective of facilitating numerous studies such as steady-state power flow, optimal power dispatch analysis, transient stability, and provision of ancillaries